Urachal Cyst in a Bitch

Background: The urachus is a tubular structure continuous with the urinary bladder and the allantois in foetal mammals. It serves as a communication between these two structures. At birth, it loses its function and undergoes atrophy by fibrous proliferation within the lumen. When this atrophy process fails at some point, congenital anomalies of the urachus occur. These anomalies are rare in animals, and to our knowledge, the urachal cyst has not yet been described in dogs. The present work is unique in that it reports a case of this congenital defect in a dog. Our aim is to increase awareness and to discuss the clinical presentation, the imaging techniques used, and the final diagnosis of this anomaly.Case: A bitch Pit Bull, 3-year-old, was presented for veterinary assistance to investigate recurrent pseudopregnancy and an irregular estrous cycle. The animal presented in good bodily condition, and the white blood count and clinical biochemistry were normal. At ultrasound, 2 tubular structures, filled by an echogenic fluid mimicking uterine topography, were found extending through the umbilical and hypogastric regions. No alterations in structure, echogenicity or echotexture of the other organs were observed, including the ovaries and uterus. On exploratory laparotomy, a cystic structure was found, with 2 segments: the larger one was on the left side, attached to the apex of the bladder by its caudal portion; the other was on the right side, attached to the spleen by its cranial portion and to the apex of the bladder by its caudal portion in connection with the left segment. The ovaries, uterus and uterine horns showed no macroscopic alterations. The structure was removed, and after analysis (macroscopic morphology, wall histopathology and biochemistry of the contained fluid), it was determined to be a urachal cyst. The animal recovered uneventfully.Discussion: Ultrasound is an important tool for the evaluation of reproductive cycle physiology and its pathologies. At first, the owner’s complaint justified a fairly straightforward evaluation and clinical management of pseudopregnancy in a very healthy animal based on the history and clinical and complementary exams. However, ultrasound examination revealed two tubular structures filled with echogenic fluid in the lower abdomen. This made the case more complex, as these were interpreted as uterine horns by three different veterinarians, leading to the possibility of pyometra. The management of this condition must be cautious, since the animal's condition could rapidly deteriorate, necessitating an exploratory laparotomy. Based on the clinical presentation, macroscopic anatomy, fluid biochemistry and histological evaluations, the diagnosis of urachal cyst was proposed. Congenital anomalies occur when the urachus fails to obliterate. Four types can be found: patent urachus, urachal sinus, urachal diverticulum and urachal cyst. The urachal cyst occurs when the urachus encompasses a cyst-like structure that is closed to the umbilicus and the bladder lumen. The urachus becomes a cystic structure since its epithelium is still intact, active and accumulating fluid, like the one analysed in this report. Most urachal cysts in humans remain asymptomatic, but when infected, they can cause focal or diffuse peritonitis and an acute abdomen. Although rare, urachal cysts can develop malignant transformation. The combination of nonspecific symptoms and the infrequent occurrence of this anomaly make its diagnosis a difficult challenge. It is commonly an incidental finding like the case reported here. Therefore, diagnostic imaging techniques, especially ultrasound, are essential for the diagnosis. To our knowledge, this is the first case report of a urachal cyst in a dog. This rare anomaly of the urachus was an incidental finding in the investigation of the reproductive problems of a female dog.